Ambassador, British Airways; FlyerTalk Posting Legend
Join Date: Apr 2012
Location: Leeds, UK
Programs: BA GGL/CCR, GfL, HH Diamond
Posts: 42,958
Applied for and got an SPG Amex card late last year and already hold a BA amex card and a gold rewards amex card. Got my bonus 20k SPG points after hitting the £1k spend right at the end of 2012, and have now transferred them from my SPG account to BAEC along with the nice bonus.
So I would say having a BA card shouldn't prevent you from getting the bonus from the SPG card.